1. Field of the Invention
The present invention relates to flow nozzles that are adapted to receive plastic melt from the injection unit of an injection molding machine and direct it into a mold cavity. More particularly, the present invention relates to an improved flow nozzle that includes a sealing member within the flow nozzle for confining the flow of plastic melt to a central passageway within the flow nozzle structure.
2. Description of the Related Art
In the injection molding of thermoplastic materials, a system is provided to convey the plastic melt supplied by the injection unit of the molding machine to the mold cavities. A key element is the injection nozzle, which is in fluid communication with the outlet of the injection unit and mates with the primary gate location (inlet opening) of the mold. The nozzle serves to convey the plastic melt from the outlet of the injection molding machine into the mold cavity, and it generally has an associated heater for maintaining the plastic melt at the desired temperature, thereby optimizing flow properties so that it fills the entirety of the mold cavity. It is particularly important that the nozzle seal effectively in the area adjacent the mold cavity to avoid leakage of plastic melt during the high pressure of injection.
Some flow nozzle structures include threaded connections between a nozzle body and a nozzle tip, which can unintentionally allow passage of some of the plastic melt into the threaded area (leakage), making it difficult to separate the parts of the nozzle for purposes of maintenance or repair. Gaps within the assembled flow nozzle that allow such leakage between parts to occur are often the result of normal manufacturing tolerances of the connected parts, as well as different rates of thermal expansion for the materials used to make the nozzle parts.
Examples of several known injection nozzle structures are disclosed in U.S. Pat. No. 2,529,146, entitled "Injection Molding Apparatus", which issued on Nov. 7, 1950, to R. Feitl; U.S. Pat. No. 4,010,903, entitled "Nozzle For Injection Molding Of Thermal Plastics", which issued on Mar. 8, 1997, to Osamu Sakuri et al.; and U.S. Pat. No. 4,266,723, entitled "Nozzle For Injection Molding Machines", which issued on May 12, 1981, to Jesus M. Osuna-Diaz. Each of the Feitl and Osuna-Diaz patents shows a structure having threaded connections of parts that because of thermal expansion and contraction could result in small gaps into which plastic melt can migrate. The Sakuri et al. nozzle includes an internally-positioned spring for maintaining contact between a needle valve and a surrounding conical cylinder cap, except when it is intended that material flow through the nozzle which, because of pressure differentials, causes the needle to move away from the cylinder cap. However, because of the intended relative movement of the parts, that structure can result in wear over a period of time, generating spaces between parts into which plastic melt can enter.
As described above, prior art nozzle constructions are typically prone to damage and seal degradation over time. In addition, plastic tends to migrate into the threaded areas, resulting in binding of the threads when disassembly for maintenance or repair is attempted. Accordingly, it is an object of the present invention to provide a flow nozzle for injection molding wherein the nozzle structure is such as to prevent the flow of plastic melt into gaps or spaces between adjacent parts. It is another object of the present invention to provide a flow nozzle for injection molding in which compressive forces are provided to maintain contacting parts in close contact, thereby preventing relative movement between the parts and potential leakage of plastic melt between the parts.